Comparison of hydroacoustic and net estimates of fish guidance efficiency of an extended submersible bar screen at John Day Dam
efficiency, fish guidance, guidance, guidance efficiency, fish passage, John Day Dam, Columbia River, intake, hydroacoustics, slope, Hydropower
Journal or Book Title
North American Journal of Fisheries Management
We compared results of the hydroacoustic and netting methods of estimating guidedand unguided fish passage and evaluated fish-guidance efficiency (FGE) of an extendedsubmersible bar screen at John Day Dam on the Columbia River. Hydroacoustic counts of guidedfish were significantly correlated with concurrent gatewell catches (r2 = 0.73; N = 39), as werehydroacoustic counts of unguided fish with fyke-net catches (r2 = 0.71; N = 39). However,hydroacoustic sampling significantly underestimated both guided and unguided fish passagerelative to netting estimates. We could not explain the underestimates by modeling hydroacousticdetectability, and the distribution of fish passage across the intake width was not skewed awayfrom transducer sampling volumes. Hydroacoustics provided relatively unbiased estimates of fishguidance efficiency (guided/(guided + unguided)) because of compensating errors in thenumerator and denominator. The best correlation between net and hydroacoustic estimates ofefficiency (r2 = 0.85; N = 40) had a slope of 0.91 when the intercept was set to zero. Precision ofhydroacoustic estimates increased 50% and the r2 of the correlation line increased 19% whenhydroacoustic sampling duration was extended from the typical netting duration of 1–2 h to 4 h.Further increases in hydroacoustic sampling duration from 5 to 9 h provided no significantimprovement in correlations. Strong correlations between estimates of FGE derived from nettingand hydroacoustic sampling are reassuring and useful because both methods have advantagesthat can be exploited to improve overall sampling effectiveness at a hydropower project. Thederivation of a universally applicable relation between hydroacoustic and physical-captureestimates of fish passage is not possible given many potential deployment-dependent biases inestimates.